The present invention relates to an engine control apparatus and method for accurately controlling the operation of the engine such as ignition, fuel injection, etc..
In order for a multi-cylinder internal combustion engine to properly operate, fuel injection, ignition and the like for each cylinder must take place at prescribed piston positions or rotational angles of the crankshaft of the engine, i.e., at the times when each piston of the engine is at prescribed positions with respect to top dead center.
FIG. 5 illustrates, in a block diagram, a conventional engine control apparatus for an internal combustion engine. The apparatus includes a signal generator 8 which generates a positional signal L in the form of pulses each indicating a corresponding cylinder, sensor means 20 including various kinds of sensors for sensing various engine operating conditions such as the engine load, the rotational speed, the engine temperature, etc., and generating an engine operation signal D indicative of the sensed engine operating conditions, an interface circuit 9, and a control means 10 in the form of a microcomputer which receives the positional signal L from the signal 8 and the engine operation signal D from the sensor means 20 through the interface circuit 9 and recognizes, based thereon, the operating condition (i.e., crank angle or rotational position) of each cylinder so that it can properly control the operating conditions such as ignition, fuel injection, etc., of the cylinders.
To this end, the microcomputer 10 includes a register means 11 for registering the positional signal L at every reference piston position of the cylinders in the form of a serial pattern, a fuel control means 13 such as a fuel injection control means for controlling the fuel supply to the respective cylinders, an ignition control means 14 for controlling the current supply to each ignition coil as well as ignition timings of the respective cylinders, a distributor control means 15 for controlling an unillustrated distributor, and a calculation and control means 12 for recognizing the operating piston position of each cylinder based on the positional signal L by making reference to the serial pattern registered in the register means 11, and controlling the fuel control means 13, the ignition control means 14 and the distributor control means 15.
FIG. 6 diagrammatically shows in more detail the construction of the calculation and control means 12. The calculation and control means 12 illustrated comprises a signal detection means 31 for detecting each reference piston position based on the positional signal L, a pulse period calculating means 32 for calculating the pulse period T of the positional signal L between the preceding two successive pulses at every reference piston position, a cylinder recognition means 33 for recognizing, based on a serial pattern P from the register means 11, to which cylinder a pulse of the positional signal L corresponds, a target control position calculation means 34 for calculating, based on the result of the cylinder recognition and the engine operation signal D, a target control position A for a cylinder at every reference piston position of the cylinder, a control time calculation means 35 for calculating, based on the pulse period T and the target control position A for the cylinder, a control time Tx for the cylinder, and a timer means 36 which is set to the control time Tx for controlling the control means 13 through 15 so as to properly control the cylinders. The timer means 36 includes a plurality of current-supply starting timers (not shown) each starting the current supply to a corresponding ignition coil for the ignition of a corresponding cylinder, and a plurality of current-supply cut-off timers (not shown) each cutting off the current-supply to a corresponding ignition coil so as to ignite a corresponding cylinder.
A typical example of the signal generator 8 is illustrated in FIG. 7. In this figure, the signal generator 8 illustrated includes a rotating plate 2 mounted on a rotating shaft 1 (such as the distributor shaft) which rotates in synchrony with the crankshaft of the engine. The rotating plate 2 has a set of first slits 3a formed therethrough at prescribed locations. The slits 3a are disposed at equal intervals in the circumferential direction of the rotating plate 2. The slits 3a, which are equal in number to the cylinders, are disposed so as to correspond to prescribed rotational angles of the crankshaft and thus to prescribed positions of each piston with respect to top dead center for sensing when the crankshaft reaches a prescribed rotational position for each cylinder. Another or second slit 3b is formed in the rotating plate 2 adjacent one of the first slits 3a at a location radially inwardly thereof for sensing when the crankshaft rotational angle is such that the piston of a specific reference cylinder is in a prescribed position.
A first and a second light emitting diode 4a, 4b are disposed on one side of the rotating plate 2 on a first outer circle and a second inner circle, respectively, on which the outer slits 3a and the inner slits 3b are respectively disposed. A first and a second light sensor 5a, 5b each in the form of a photodiode are disposed on the other side of the rotating plate 2 in alignment with the first and the second light emitting diode 4a, 4b, respectively. The first light sensor 5a generates an output signal each time one of the outer slits 3a passes between the first light sensor 5a and the first light emitting diode 4a. Also, the second light sensor 5b generates an output signal each time the inner slit 3b passes between the second light sensor 5b and the second light emitting diode 4b. As shown in FIG. 8, the outputs of the first and second light sensors 5a, 5b are input to the input terminals of corresponding amplifiers 6a, 6b each of which has its output terminal coupled to the base of a corresponding output transistor 7a or 7b which has the open collector coupled to the interface circuit 9 (FIG. 5) and the emitter grounded.
Now, the operation of the above-described conventional engine control apparatus as illustrated in FIGS. 5 through 9 will be described in detail with particular reference to FIG. 9 which illustrates the waveforms of the output signals of the first and second light sensors 5a, 5b.
As the engine is operated to run, the rotating shaft 1 operatively connected with the crankshaft (not shown) is rotated together with the rotating plate 2 fixedly mounted thereon so that the first and second light sensors 5a, 5b of the signal generator 8 generate a positional signal L which comprises a first and a second signal L1, L2 each in the form of a square pulse. The first signal L1 is a crank angle signal called SGT signal and has a rising edge corresponding to the leading edge of one of the outer slits 3a (i.e., a first prescribed crank angle or position of a corresponding piston) and a falling edge corresponding to the trailing edge thereof (i.e., a second prescribed crank angle of the corresponding piston). In the illustrated example, each square pulse of the SGT signal L1 rises at the crank angle of 75 degrees before top dead center (a first reference position B75 degrees) of each piston, and falls at the crank angle of 5 degrees before top dead center (a second reference position B5 degrees).
The second signal L2 is a cylinder recognition signal called SGC signal, and has a rising edge corresponding to the leading edge of the inner slit 3b and a falling edge corresponding to the trailing edge thereof. The SGC signal L2 is issued substantially simultaneously with the issuance of an SGT signal pulse corresponding to the specific reference cylinder #1 so as to identify the same. To this end, the inner slit 3b is designed such that it has a leading edge which corresponds to a crank angle before the first reference angle of the corresponding SGT signal pulse (i.e., a crank angle greater than 75 degrees before TDC), and a trailing edge corresponding to a crank angle after the second reference angle of the corresponding SGT signal pulse (i.e., a crank angle smaller than 5 degrees before TDC). Thus, actually, the rising edge of an SGC signal pulse occurs before that of a corresponding SGT signal pulse, and the falling edge of the SGC signal pulse occurs after that of the corresponding SGT signal pulse, so the SGC signal has a high level at the reference piston positions of 75 and 5 degrees BTDC.
The two kinds of first and second signals L1, L2 thus obtained are input via the interface circuit 9 to the calculation and control means 12 of the microcomputer 10 which recognizes, based on these signals, the specific reference cylinder #1 and the operational piston positions (i.e., crank angles or rotational positions) of the remaining cylinders #2 through #4, whereby various engine operations such as ignition timings, fuel injection timings, etc., are properly controlled.
Specifically, the signal detection means 31 of the calculation and control means 12 detects the positional signal L comprising the SGT signal L1 and the SGC signal L2 and generates a serial pattern P which takes the high or low level (i.e., 1 or 0) of the SGC signal L2 at the respective reference piston positions (i.e., 75 and 5 degrees BTDC) of the SGT signal L1. The serial pattern P thus formed is registered into the register means 11. The pulse period calculation means 32 calculates the pulse period T of the SGT signal L1 between prescribed reference piston positions. The cylinder recognition means 33 recognizes, based on the serial pattern P stored in the register means 11, the operating position of a piston in each cylinder, and outputs the result of such cylinder recognition to the target control position calculation means 34 which also receives the engine operation signal D from the sensor means 20 through the interface circuit 9.
The target control position calculation means 34 calculates, based on the result of the cylinder recognition and the engine operation signal D, an optimal target control position A such as an optimal ignition timing, an optimal fuel injection timing, etc., for a cylinder corresponding to the present pulse of the SGT signal L1, and outputs the thus obtained target control position A to the control time calculation means 35 which also receives the pulse period T from the pulse period calculation means 32.
The control time calculation means 35 calculates, based on the pulse period T and the target control position A for the cylinder, an appropriate control time Tx for the cylinder and accordingly sets the timer means 36. For example, in order to control the current-supply starting timing and the current-supply cut-off or ignition timing for a cylinder, a corresponding current-supply starting timer of the timer means 36 is set to a current-supply starting time Tsx (x=1 through 4 for cylinders #1 through #4), and a corresponding current-supply cut-off timer of the timer means 36 is also set to a current-supply cut-off or ignition time Tox (x=1 through 4 for cylinders #1 through #4), so that they control the fuel control means 13, the ignition control means 14 and the distributor control means 15 at the respective points in time thus set so as to distribute optimal control signals to the cylinder.
However, the current-supply starting time Tsx and the current-supply cut-off time Tox for a cylinder are set at each first reference piston position and at each second reference piston position, respectively, of a corresponding cylinder, and they, once set, are not updated until the following first or second reference piston position for the corresponding cylinder comes. As a result, in the event that the pulse period T of the SGT signal L1 sharply varies due to a sudden change in the number of revolutions per minute of the engine, control accuracy is considerably reduced for cylinders for which the control means 13 through 15 have to wait relatively extended periods of time until they begin to operate at set points in time. In particular, at high rotational speeds of the engine, a current supply period between a current-supply starting time and a current-supply cut-off time for a cylinder becomes longer relative to the pulse period T of the SGT signal L1 than at low speeds, so with a multi-cylinder engine having many cylinders, the control times for the respective cylinders may overlap, thus making the above control operations much more difficult and complicated. This necessarily results in a critical problem of substantial reduction in control accuracy.